Amplitude-modulated signals are still conventional in airborne communications systems. A major problem with the use of such signals is that, in the case of a random simultaneous transmission of signals, for example, by two aircraft, the relatively weaker signal arriving in the receiver remains undetected. This can lead to errors relevant to safety.
A method in which a received signal is distorted in a non-linear manner and then transformed into the frequency domain in order to detect such double transmissions is known. Symmetrical spectral components in the distorted spectrum are then determined and removed. On the basis of still remaining signal components, an inference is then made about the presence of a simultaneously transmitted second signal. For example, the German published patent application DE 10 2011 080 999 A1 discloses a method with non-linear distortion, as described above.
However, this method is disadvantageous because it requires a large computational effort as a result of the non-linear distortion. This is also problematic when using CLIMAX operating mode. It is not capable of distinguishing between several transmitters in the case of the common-wave operation of the CLIMAX system and an actual double transmission worthy of detection.